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Monitoring unusual events and non indigenous species
(Edwards et al, 2001)
The introduction of non-indigenous marine plankton
species can have considerable ecological and economic
impact on regional seas. Efforts to monitor invasive
marine species are at best fragmented, as they
are typically only noticed when the species reaches
nuisance status, so there are few case histories
of their spatial and temporal expansion. In recent
years there were a number of species recorded
in the CPR survey that were outside their expected
range. These included Penilia avirostris (a
cladoceran), Stomatopoda (mantis shrimp) and Clausocalanus
sp. These three species are more commonly found
in the warmer waters of the Bay of Biscay and
the Mediterranean Sea. Their appearance in the
North Sea may indicate a significant environmental
change.
The CPR survey has been used to trace the expansion
and subsequent persistence of the large diatom,
Coscinodiscus wailesii, which was first
recorded in the English Channel in 1977. C.wailesii
was originally known only from the Pacific coast
of North America, and in Chinese and Japanese
waters of the North Pacific. It is presumed that
it made its way from its native seas via the ballast
water of international ships. Since its first
appearance it has become a significant member
of the diatom community and is now well established
in the continental shelf seas of NW Europe. In
the southern North Sea it may now reach such high
abundance that it can dominate the phytoplankton
biomass. The ecological importance of such invasive
species can therefore have potential ecosystem
effects by out-competing native species for resources
and space, reducing biodiversity, and effecting
the exploitation of native herbivores (Edwards
et al., 2001).
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The large centric diatom Cosinodiscus
wailesii. |
Monitoring the long-term
response of plankton to global change (Reid et
al, 1998)
The CPR time series provides
a unique opportunity to assess the impact of the
increase in global temperature over the last century
and the effect of this on the base of the marine
food web. 'Phytoplankton colour' is a visual index
of chlorophyll derived from the intensity of the
green colouration of the CPR filtering silk. An
increasing trend in 'phytoplankton colour' is
evident in the North Sea and central north-east
Atlantic between 520N and 580N, with evidence
for a step-wise increase after the mid-1980s (Reid
et al., 1998). The pattern of increase in these
areas generally showed two phytoplankton peaks
from 1948-1988, corresponding to a spring and
autumn phytoplankton bloom. Thereafter, the two
peaks have merged, to show a continuous bloom
from March to almost December each year. The response
is not uniform throughout the North Atlantic,
with a somewhat inverse pattern for the northern
northeast Atlantic, showing a general decrease
in 'phytoplankton colour' since the mid-1980s.
At this time this area tended to experience colder
surface temperatures. These changes may be a response
by marine vegetation to climate forcing. If so
they are likely to have important implications
for Co2 fluxes and the productivity of the North
Atlantic.
Latitudinal change in copepod distribution (Beaugrand
et al, 2002)
Recent work on the CPR data has
provided evidence of large-scale changes in the
biogeography of calanoid copepod crustaceans.
In the eastern North Atlantic Ocean and European
shelf seas, we have observed strong biogeographical
shifts in all copepod assemblages with a northward
extension of more than 10° latitude of warm-water
species associated with a decrease in the number
of colder-water species. These biogeographical
shifts are in agreement with recent changes in
the spatial distribution and phenology detected
for many taxonomic groups in terrestrial European
ecosystems and are related to both the increasing
trend in Northern Hemisphere temperature and the
North Atlantic Oscillation. The observed biogeographical
shifts may have serious consequences for exploited
resources in the North Sea, especially fisheries
(Beaugrand et al., 2002). More
information on this article?
Increased incidence of
winter phytoplankton blooms in the northwest Atlantic
(Johns et al 2003)
Sampling by the Continuous Plankton
Recorder survey (CPR) over the northwest Atlantic
from 1960-2000 has enabled long term studies of
the phytoplankton community, highlighting various
changes. Analysis of the index of phytoplankton
colour (an index of phytoplankton biomass) revealed
an increase over the past decade especially during
the winter months (December – February). Multiple
linear regression models were used to examine
this change, where the results indicated that
the winter phytoplankton community composition
changed markedly in the period 1991-2000, compared
to the 1962-1978 period.
The dinoflagellate species Ceratium arcticum
was a significant member of the modified phytoplankton
community, with pronounced large winter blooms
and decreased autumnal levels occurring in the
period 1991-2000. Also its contribution to the
phytoplankton colour index value has increased
significantly.
Other dominant species in the phytoplankton community
include Thalassiosira spp which increases
in abundance over the examined time period although
its contribution to the phytoplankton colour index
decreased in the 1990s.
It is suggested that the response of C. arcticum
is probably a result of previously reported changes
in stratification in the northwest Atlantic, due
to dynamic hydro-climatic (freshening and cooling)
events, and these have an effect on large-scale
processes such as the Labrador Current. Changes
in the Labrador Current have altered the annual
structure of stratification. Work by Jo Craig
et al (Dept. Fisheries and Oceans, Canada) indicates
a change in stratification on the inner Newfoundland
Shelf, with an index increasing significantly
over the past decade. It is likely that haline
stratification plays an important part in
C. arcticum abundance through a delay in
the breakdown or initiation of an earlier stratified
layer, although the exact mechanisms are not known.
The massive abundance of C. arcticum
in 1996, where it contributed to almost 47% of
the total recorded phytoplankton community corresponded
to the freshest Labrador seawater on record.
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